Question: Which of these numbers is prime? ${39,\ 45,\ 77,\ 83,\ 92}$
Explanation: A prime number has exactly two factors: 1 and itself. The factors of 39 are 1, 3, 13, and 39. The factors of 45 are 1, 3, 5, 9, 15, and 45. The factors of 77 are 1, 7, 11, and 77. The factors of 83 are 1 and 83. The factors of 92 are 1, 2, 4, 23, 46, and 92. Thus, 83 is a prime number.